Method for beneficiating clay by flotation of colored impurities



United States Patent "ice U.S. Cl. 209-5 6 Claims ABSTRACT OF THEDISCLOSURE Colored titaniferous impurities in clay are removed from theclay by froth flotation of a sodium silicate dispersed pulp of the clayin the presence of flotation reagents selective to the flotation of thecolored impurities and a small amount of a water-soluble aluminum saltor manganous salt.

RELATED APPLICATIONS This application is a continuation-in-part ofapplicants copending application, Ser. No. 415,503, filed Dec. 2, 1964,now Patent No. 3,337,048, entitled Method for Beneficiating Clay byFlotation.

BACKGROUND OF THE INVENTION Clay, especially kaolin clay, is widely usedas a pigment for coating paper. For such use, the value of the clay isdependent upon its whiteness or brightness since this property affectsthe appearance of clay-coated sheet material. High-grade coating clayshave brightness values of at least about 86% to 87% when the brightnessis determined by a light reflectance method hereinafter described. Smalldifferences in brightness values of clays represent significantdifferences in the utility of the clays. Thus, a clay that has abrightness of 91.0% is markedly superior to a clay having a brightnessof 89.0% or even 90.0%.

Some clays, especially certain foreign primary kaolin clays, possessadequate brightness for paper coating use after being beneficiated onlyto the extent that coarse agglomerates and grit are removed. Otherclays, such as the sedimentary kaolin clays, as exemplified by Georgiakaolin clay, normally contain an appreciable quantity of finely dividedcolored impurities which detract significantly from the usefulness ofthe clays. These sedimentary clays, after degritting and fractionationto remove oversize, have a brightness which is far below the brightnessvalues of high-grade coating clays.

The colored impurities that account for the low brightness ofsedimentary kaolin clays include ferruginous matter. This constituentcan be removed at least in part from the clay by chemical bleachingmethods, such as with hydrosulfurous compounds which solublize theferruginous matter so that it can be removed from the clay. Sedimentarykaolin clays usually also contain anatase, which is a yellowtitaniferous impurity that has a very detrimental effect on the claybrightness. This type of impurity is substantially unaffected by thechemical bleaches used by the clay industry. To remove coloredtitaniferous impurities, it has been necessary to employ froth flotationin the presence of flotation reagents which bring about the selectiveflotation of the titaniferous matter from the clay. The flotationbeneficiated clay is then treated with chemical bleaching reagents tosolubilize and eliminate undesirable ferruginous matter. The flotationof the titaniferous matter from the clay can be achieved by dispersingthe clay in water, incorporating 3,462,013 Patented Aug. 19, 1969 ahigher fatty acid, such as tall oil acids, aerating the system andwithdrawing a froth which is a concentrate of the yellow titaniferousimpurities originally associated with the clay. Especially good resultshave been obtained with ultraflotation, which is a particular type offlotation process. In this type of flotation process, described in U.S.2,990,958 to Ernest W. Greene et al., a substantial amount of finelydivided insoluble particulate matter, usually finely divided calcite, isincorporated into the aqueous clay dispersion along with the fatty acidcollector reagent. The added particulate matter, which is alsoreagentized by the fatty collector reagent, enhances the flotation ofthe finely divided colored impurities and reports in the froth alongwith the colored impurities. Ultraflotation in conjunction with chemicalbleaching has resulted in the commercial availability of 90% to 91%brightness Georgia kaolin clay from clay crudes having brightness valuesless than To brighten clay by flotation and chemical bleaching tooptimum brightness values, it has been found that it is essential toachieve complete dispersion of the clay by means of sodium silicate or amixture of soluble carbonate and sodium silicate before subjecting theclay to flotation. It has been necessary, however, to carefully controlthe quantity of sodium silicate used. Even a small excess of the sodiumsilicate has been found to affect adversely the results of the flotationoperation. In many cases, adequate control of dispersant dosage has beenvery difficult because of individual differences in the dispersantdemand of different crudes, even crudes from different localities withinthe same mine.

In the case of gray (hard) kaoline crudes, the problem of controllingdispersant dosage so as to disperse the clay for flotation withoutdepressing colored impurities can be especially troublesome. Thedispersant requirements of gray kaolin crudes vary to a great extentwith the age of the mined crudes and a crude which has been stored forseveral months after being mined may require substantially more sodiumsilicate than the same crude would have required if it had beendispersed immediately after being mined.

SUMMARY THE INVENTION An object of this invention is to improve theeffectiveness of froth flotation as a method for removing coloredimpurities from clay.

One specific object is to buffer the effect of sodium silicatedispersant in clay flotation so that the clay is not so sensitive to thequantity of alkali silicate dispersant and small amounts of excessdispersant will not adversely affect flotation results.

Another object is to improve the brightness of flotation beneficiatedclays.

Still another object is to provide a process for brightening gray kaolinclays to brightness values comparable to those of high-grade whitecoating clays.

I have discovered that difficulties resulting from the possible use ofexcessive quantities of sodium silicate dispersant may be obviated byadding a small amount of a water-soluble salt of aluminum or awater-soluble manganous salt to a sodium silicate dispersed pulp ofkaolin clay, preferably before the clay pulp is conditioned for frothflotation with reagents selective to the flotation of coloredimpurities, especially titaniferous impurities.

Thus, in accordance with the present invention, the selective frothflotation of titaniferous impurities from a sodium silicate dispersedpulp of discolored kaolin clay is carried out in the presence of anadded watersoluble aluminum or manganous salt. As a result of thepresence of the polyvalent metallic salt additive, the beneficiated claywill contain no more Ti0 and be at least as bright as the beneficiatedclay would be if optimum sodium silicate dosage were used, this being arare possibility. If, by chance, the pulp is formulated with an opti mumquantity of dispersant, the salt additive will have no deleteriouseffect. In fact, in some cases, a further improvement in titaniaflotation may be realized.

DESCRIPTION OF THE INVENTION The preferred aluminum salts that are usedin putting the invention into practice are aluminum sulfate, nitrate,chloride, acetate and mixtures thereof. The use of hydrated salts iswithin the scope of the invention. Ammonium and potassium alums are alsosuitable. Soluble manganous salts include the nitrate, chloride, sulfateand acetate salts. Mixtures of manganese salts and aluminum salts areuseful in carrying out the invention.

The quantity of salt that is employed is usually within the range ofabout 0.1 to 2.0 pounds per ton of clay, with especially good resultsbeing obtained with 0.4 to 0.8 pound per ton. When too little salt isused, the effect of its use may not be appreciable. When too much saltis used, clay recovery may be reduced appreciably as a result of theactivation of the clay by the additive. With very large excesses ofsalt, fluocculation of the pulp will occur. This, of course, isundesirable since the pulp must be well dispersed during conditioningand flotation.

The preferred method for adding the salt involves the incorporation ofan aqueous solution of the salt to a solution of the sodium silicatedispersant before the clay is dispersed with the sodium silicate. Theconcentration of the salt solution is not critical. Concentrationswithin the range of 1% to 20% by weight are suggested. In carrying outthe form of the invention wherein the salt is incorporated in the formof a hydrosol, the solution of salt is added to an aqueous solution ofthe sodium silicate until a stable hydrosol is formed by the addition ofthe salt. The hydrosol contains a colloidally dispersed precipitate,probably a complex sodium aluminum silicate or similar manganesecompound. The hydrosol has a turbid appearance, exhibits the Tyndallphenomenon and is free from fiocs. The use of such a hydrosol in clayflotation is described and claimed in my copending application, Ser. No.415,503, filed Dec. 2, 1964, now Patent No. 3,337,048. When using thesalt additive in the form of a hydrosol, the clay product may bebrighter and appreciably lower in titania content than the beneficiatedclay would be using an optimum quantity of dispersant.

The following table contains data illustrating the effect of addition ofvarious quantities of aluminum sulfate to a solution of brand sodiumsilicate (the registered trademark of a solution reported to contain9.16% Na O, 29.5% SiO and about 62% H O, weight basis). The datarepresent results obtained by slowly adding a 1% (weight basis) aqueoussolution of alum with agitation into a aqueous solution of 0 brandsodium silicate (5 parts by weight 0 brand sodium silicate to 100 partsby weight water) and allowing the composition to stand for the periodsof time indicated.

EFFECT OF ADDITION OF ALUM TO A DILUTE SODIUM SILICATE SOLUTION Ml. of1% alum Percent solution per alum, based 100 ml. 5% on anhysodiumsilidrous weight; pH at;

catc solution of sodium Tiuic end of silicate Rtsult (hr.) time 100 50Appreciablc fl0ccu 1 9. 5

lation.

While optimum removal of the finely divided titania impurities from theclay is usually realized by incorporating the polyvalent metal salt withthe sodium in the form of a hydrosol, as described above, substantialimprovements are also obtained by adding the salt after the clay ha beendispersed with sodium silicate but before the dispersed pulp is aeratedand a froth produced. Thus, when the discolored clay has already beendispersed in water with a quantity of sodium silicate somewhat is excessof the sodium silicate that is used for optimum flotation results, theTiO content of the clay after flotation will be lower, frequentlysignificantly lower, if a small amount of polyvalent metallic salt suchas alum is added to the sodium silicate dispersed pulp at any timebefore the pulp is subjected to froth flotation. However, it is verydesirable to incorporate the salt before oiling reagents (e.g., fattyacids) are added to the dispersed pulp and to agitate the pulp after thealuminum salt is added. When the flotation reagents include a solidparticulate carrier, such as calcite, as described in U.S. 2,990,958, orfinely divided polymeric particles, as described in U.S. 3,224,- 582,the salt may be incorporated after addition of the carrier and beforeaddition of buffering salts such as ammonium sulfate and flotation oils(fatty acid, etc.) since the effect of the aluminum or manganese saltmay be more pronounced when added at such point. However, even when thealuminum salt is added after the carrier, pH buffer and flotation oils,the use of the aluminum or manganese salt will be of appreciablebenefit. The salt may also be incorporated into a pulp of the claybefore addition of all or a portion of the dispersant.

As mentioned, the polyvalent metallic salt is employed as a flotationreagent in a pulp of discolored clay which is dispersed withwater-soluble sodium silicate, or preferably, a mixture of water-solublecarbonate and sodium silicate. Sodium silicates having Na O to SiOweight ratios of 1:160 to 123.75 are water-soluble and useful ineffecting the dispersion of an aqueous clay pulp. The quantity of sodiumsilicate required to disperse any clay pulp depends upon the nature ofthe clay and the possible use of soluble carbonate salts. An optimumquantity may vary very substantially with crudes from the same portionof a mine, as mentioned above. With most clays, sodium silicate isemployed in amount within the range of 0.5 to 4.0 pounds anhydroussodium silicate per ton of clay. Most usually, 1.0 to 3.0 pounds per tonanhydrous sodium silicate is used. Using the commercially available 0brand sodium silicate (which contains about 62% water), about 2.0 to10.0, and preferably 3.0 to 6.0 pounds, of the solution is used forevery ton of clay. Preferably, a water-soluble carbonate salt,especially sodium carbonate or ammonium carbonate, is added to the claypulp in amount of 2.0 to 10.0 pounds per ton of clay before addition ofthe sodium silicate (or hydrosol made by addition of metallic salt to adilute solution of the sodium silicate). With white clays, ammoniumcarbonate is the preferred carbonate. With gray clays (clays similar incomposition to the white clays but having a distinctly gray tinge),sodium carbonate is preferred.

The flotation pulps should be prepared with about 10% to 30% claysolids.

The flotation reagents used in carrying out the process of thisinvention include fatty acid reagents which are selective to the titaniaimpurities in the clay. The flotation reagents used in ultraflotationare preferred. As mentioned in U.S. 2,990,958 to Ernest W. Greene etal., reagents for ultraflotation concentration include, in addition tohigher fatty acid, especially a mixture of resin acid and fatty acid(tall oil acids), a substantial quantity of finely divided auxiliaryparticles different from the clay and rendered floatable by the oilsused to float selectively the titania impurities. Minus 325 mesh calciteis preferred although other finely divided minerals 01' polymericparticles may be employed. Additional quantities of sodium silicate canbe incorporated into the pulp after addition of the auxiliary particlesif the addition of the carrier particles results in flocculation of thepulp. Am-

5 monium hydroxide can be used to adjust the pH to adesired level ofabout 8.0 to 8.5. The pH can be buffered, as by the addition of ammoniumsulfate when ammonium hydroxide is used to adjust pH. Flotation iscarried out in an alkaline pulp, producing a froth which is aconcentrate of impurities in the clay intimately mixed with the finelydivided additive. The beneficiated clay, in the form of a dispersedpulp, reports in the machine discharge product. The recovery ofbeneficiated clay can be. improved by refloating the froth product oneormore times.

EXAMPLES The following examples are given to contribute to a betterunderstanding of the present invention and to illustrate its benefits.

Examples I and II, which follow, illustrate the application of myprocess to the flotation beneficiation of white sedimentary Georgiakaolin clay (Washington County clay). Representative samples of theminus 325 mesh portions of this crude contained about 2.6% TiO and had abrightness of about 80% before being beneficiated by flotation andbleaching.

In beneficiating the white clay, the following general dispersion andflotation procedures were used. In some cases, these procedures weremodified as described in the examples. In describing the procedures, allreagents are reported on a weight basis and represent pounds per ton ofdry clay unless otherwise indicated. The TiO analyses of products arereported on a volatile-free weight basis and were based upon the weightof products obtained after heating to constant weight at 1800 F.

Dispersion-white clay Twelve hundred and fifty grams of dry'clay wasdiluted with soft water to 30% solids, weight basis, and transferred toa Fagergren flotation cell. When used, sodium carbonate or ammoniumcarbonate was added as a 5% (weight basis) aqueous solution and inamount to provide a desired quantity, typically 2.0 to 6.0 pounds sodiumor ammonium carbonate, per ton of clay. The pulp was agitated withoutaeration for 1 minute. A 5% aqueous solution of brand sodium silicatewas prepared by adding parts by weight 0 brand to 100 parts by weightwater. The 5% solution was added to provide the desired quantity ofdispersant, typically 3.0 to 8.0 pounds 0 brand per ton of clay. Whensodium or ammonium carbonate was used, the dilute sodium silicatesolution was incorporated immediately after agitating the pulp for aminute with the carbonate. After addition of the sodium silicatesolution, thepulp was agitated for 30 minutes in the Fagergren flotationcell and the pH recorded. The slip was then degritted by passing itthrough a 325 mesh screen.

Ultraflotation-white clay A portion of the pulp containing 750 grams ofthe degritted clay (dry clay basis) was diluted with 250 ml. soft water,112.5 grams of minus 325 mesh calcite having an average particle size ofabout 5 microns Drikalite) was added and agitated without aeration for 1minute. The pulp in the conditioner was at about 25% solids, weightbasis. Forty-five ml. of a 5% ammonium sulfate solution was added andthe pulp was conditioned for /2 minute. An emulsion of the followingcomposition was then added to the pulp and conditioned for 17 minutes:250 ml. of soft water, 30 ml. of a 2 /2% aqueous solution of ammoniumhydroxide, 137 drops of a mixture of equal parts of crude tall oil acidsand a 50% solution of neutral calcium petroleum sulfonate in mineral oilsupplied under the registered trademark Calcium Petronate. After 5minutes conditioning time had elapsed, 111 drops of lubricating oil(Eureka M) were added. The reagent quantities represented by the reagentadditions are as follows:

Reagent- Lbs./ ton Calcite ...4- 300 (NH SO 6.0 NH.,,OH 2.0 Tall OilAcids 4.5 Calcium Petronate 4.5 Eureka M Oil 8.0

1 Aqueous emulsion.

The pH of the pulp at the end of conditioning was typically 8.5-8.8.

The conditioned pulps were subjected to aeration and froth flotation ina 1000 cc. Air Flow flotation cell, removing a froth product for 10minutes. The froth products were refloated three times without additionof reagents, producing three products in each case: a froth product(F.P.)'; a first machine discharge product (MD-1); and a combinedmachine discharge product (-MD2,3,4). MD-l typically contained about6.5% solids and MD-2,3,4 about 2.5% solids. The machine dischargeproducts were analyzed by a standard chemical method for TiO Brightnessvalues of products were determined by TAPPI Standard Method T-646 m-54,as described on pages 159A and 160A of the October 1954 issue of TAPPI(a monthly publication of the Technical Association of the Pulp andPaper Industry). The method measures the light reflectance of a claysample and thus gives a quantitative indication of its brightness orwhiteness.

Bleachingwhite clay The machine discharge products were flocced byaddition of sulfuric acid in amount to reduce the pH to 2.5. The floccedclay was bleached with zinc hydrosulfite solution, following typicalpractice of the industry. The clay was then filtered. The brightness ofthe clay after being bleached was measured and compared to thebrightness of the clay after flotation but before bleaching for thepurpose of determining the further improvement in brightness resultingfrom the chemical bleach.

EXAMPLE I To illustrate the effect of the quantity of dispersant on theflotation of titania impurities from the Washington County kaolin clay,flotation tests were carried out by the procedure above described withcombinations of sodium or ammonium carbonate and sodium silicatedispersant, using from 3.0 to 8.0 lbs/ton 0 brand sodium silicate. Theresults, summarized in Table I, show that when the pulp contained toomuch sodium silicate (8.0 lbs/ton with this particular clay), thebeneficiated clay product was more discolored and contained more Ti0than when smaller quantities (3.0 to 5.0 lbs./ ton) of the sodiumsilicate were used. These results therefore indicate that more titaniawill be removed by flotation of this particular clay when less than 8.0lbs./ ton of sodium silicate is used. However, as mentioned above, it isnot always practical or possible to disperse a clay pulp for flotationwith fair assurance that the particular dispersant dosage is such as toassure optimum flotation with the reagents that are used.

0 brand Unbleached Properties of MD-l sodium brightness, Wt. percentNaZCOQ (NHmCOa silicate percent TiO 2 7 EXAMPLE 11 This exampleillustrates the desirability of adding an aluminum salt to the sodiumsilicate dispersed clay pulp before the pulp is subjected to flotation.The clay that was used contained 2.60% TiO and was the same crude usedin the previous example. In this example tests were carried out with 8.0pounds per ton of brand sodium silicate dispersant, a quantity which, asshown in the previous example, did not result in optimum titania removalby froth flotation. In all cases, 25 ml. of a ammonium carbonatesolution was added to 1250 grams of the Washington County crudepreviously blunged in water to 30% solids and the dispersant compositionwas then added to the carbonate-treated slip and conditioned for 1minute.

In one experimental test, the alum was incorporated by mixing 100 ml. of5% 0 brand sodium silicate solution (5 parts by weight 0 brand to 100parts by weight in the first machine discharge products contained 0.19%to 0.20% TiO when the alum was added after the clay pulp was dispersedwith 8.0 lbs./ ton sodium silicate. These results compare favorably tothe 0.18% to 0.19% TiO products produced by using smaller quantities ofsodium silicate (see Table I) and were distinctly superior to theresults obtained with 8.0 lbs/ton sodium silicate without any alumaddition. Similar benefits were observed in studies of the properties ofthe combined machine discharge products. I

Thus, it was found that by adding alum to the pulp at any time beforeaeration and flotation, the titania removal was always better with apulp containing a slight excess of sodium silicate dispersant.

Data in Table II for the recovery of clay in the combined machinedischarge products indicate that the use of alum did not substantiallyimpair recovery unless the TABLE II.EFFEC'I ON FLOIA'IION OF METHOD OFALUM ADDITION TO CLAY PULP Slip treatment, lbs/ton MD-1 MD-I4 0 brandsodium Percent Percent Percent Percent (NHihCO; silicate 3Alg(SO4)3.l-8H3O Method of alum addition wt. T10 Wt. TiO

2.0 8.0 0.4 Alum and sodium silicate added as mixture 47.9 0.15 91,00,17

(hydrosol).

2,0 8.0 0.4 Alum and sodium silicate added as mixture 41.7 0.15 37.7 0.1

(hydrosol) 2.0 0.4 Sodium silicate added first followed by alum 48.50.19 91.3 0,

after one minute.

2.0 8. 0 0. 4 Alum added after calcite flotation reagent 51. 4 0, 20 92.2 0, 20

2.0 8. 0 0. 4 Alum adtded after emulsified fatty acid flotation 44. 4 0.19 89. 4 0. 20

reagen 2.0 8. 0 Control, no alum added 51. 3 0.23 91.8 0, 22

1 Conditioned for 30 minutes. 2 Conditioned for 60 minutes.

water) with 25 ml. of 1% alum solution for minutes, adding the resultingstable hydrosol to the clay pulp and agitating without aeration for 30minutes. Another test was carried out in the same way but theconditioning time was 60 minutes. In still another test, the sodiumsilicate and alum were added separately. In that case after addition ofammonium carbonate solution to the 30% solids clay pulp and one minuteconditioning, 100 ml. of the 5% solution of 0 brand sodium silicate wasadded to the pulp and conditioned for 1 minute. Twenty-five ml. of 1%aqueous alum solution was then added and conditioned for 29 minutes. Inother tests, alum was added either after the calcite carrier and beforeaddition of emulsified fatty acid reagent or after the emulsified fattyacid reagent. In all cases the pulp was degritted over a 325 mesh screenafter the dispersant treatment and before being reagentized forultraflotation concentration with calcite carrier and emulsified fattyacid reagent. The pH of the pulps were about 8.1 after dispersion anddegritting. After addition of the emulsified flotation reagents, the pHof the pulps were 85:0.1.

Analyses were made on MD-l and on composites of MD-l and MD-2,3,4(indicated as MD-l-4), with the results summarized in Table II.

The data in Table II show that, using 2.0 lbs/ton ammonium carbonate,8.0 lbs/ton sodium silicate and no alum additive, the beneficiated clayin the first machine discharge product (MD1) contained 0.23% TiO and thebeneficiated clay in the combined machine discharge products contained0.22% TiO As noted in Table I, the MD- 1 products contained only 0.18%to 0.19% TiO when smaller quantities of sodium silicate had beenemployed to disperse this clay. Data in Table II show that when the alumwas added as a hydrosol, the TiO content of the MD-l was only 0.15% inspite of the fact that 8.0 lbs./ ton sodium silicate had been used inthe dispersion step. Thus, the titania removal was even better when thehydrosol was used in spite of the fact that an excessive amount ofdispersant had been used in preparing the clay for the selectiveflotation of colored impurities.

Data in Table II also show that the beneficiated clay 8 Wet basis.

alum was used as a hydrosol and conditioning time was EXAMPLE III Thefollowing example illustrates the benefits of carrying out the flotationbeneficiation of a gray Georgia kaolin clay in the presence of an addedaluminum salt or manganese salt.

The same procedures employed in dispersing and floating the whiteWashington County clay were used with the gray kaolin clay with thefollowing exceptions. Sodium carbonate was incorporated into the claypulp as a 5% aqueous solution in amount of 8.0 lbs./ton of clay crudeand conditioned for 30 minutes before addition of the solution of sodiumsilicate or hydrosols formed by adding alum or manganous sulfate to thesodium silicate solution. Addition of the sodium carbonate increased thepH of the clay pulp to about 5.8. In a control test, sodium silicate wasused to disperse the sodium carbonate treated pulp in amount of 5.0pound 0 brand per ton of clay. In another test, a 1% alum solu tion wasmixed into the 5% sodium silicate solution to form a hydrosol and thehydrosol was conditioned with a portion of the gray clay pulp for 20minutes. This addition corresponded to the use of 5 .0 pounds of 0 brandsodium silicate per ton of clay and 0.4 pound of Al (SO .18H O per tonof the clay. In still another test, a 1% aqueous solution of MnSO .H Owas incorporated into 5% sodium silicate solution and the result inghydrosol employed in amount to provide 0.4 pound MnSO .H O per ton ofclay and 5.0 pounds of 0 brand sodium silicate per ton of clay.

The dispersed clay pulps were separately fractionated beforeultraflotation by means of a centrifuge and a fine fraction recovered asan aqueous pulp. The quantity of flotation reagents used with each pulpof the fine fraction of gray clay varied somewhat from the quantityemployed with the white clay because previous experience had shown thatsuch a variation in reagent quantity would be necessary to achieveoptimum results. The reagents used with the gray clay were as follows:

Reagent Lbs./ ton Calcite (minus 325 mesh) 600 (NH SO 6.0 NH OH 3.0 TallOil Acids 6.2 Calcium Petronate" 6.2 Eureka M Oil 8.0

1 Aqueous emulsion.

Conditioning time was 30 minutes and the flotation procedure was thesame used with the white clay.

A further variation was that after the flotation beneficiated gray claywas flocced with sulfuric acid, it was oxidized by treatment with asolution of potassium permanganate before being bleached with zinchydrosulfite. The permanganate treatment was carried out by adding a 1%aqueous solution of potassium permanganate to the machine dischargeproduct in amount of 5 pounds KMnO per ton of clay and agitating for 60minutes. In some tests, the permanganate treatment and zinc hydrosulfitetreatments were carried out at about 190 F. (The use of a permanganatetreatment before reducing bleach in the brightening of clay is disclosedand claimed in US. 3,353,668 to James B. Duke patent application, Ser.No. 330,634, filed Dec. 16, 1963, by James B. Duke, which is acontinuation-in-part of Ser. No. 236,685, filed Nov. 9, 1962, nowabandoned.)

When metallic salt was not present (the control experiment), thebrightness of the flotation beneficiated, bleached gray kaolin clay was90.6%, as compared to a brightness of 79.8% for a similar size fractionof the crude. When the flotation was carried out in the presence of thealum, however, product brightness was increased to 91.2%, a valuecomparable to that of the best imported kaolin clays and the bestbeneficiated domestic white kaolin clays. When flotation was carried outin the presence of manganous sulfate, clay brightness after bleachingand flotation was 91.5%. These results show, therefore, that theflotation was more effective with the gray clay when it was carried outwith an aluminum or manganese salt additive.

I claim:

1. In a process for removing colored titaniferous impurities from kaolinclay by froth flotation wherein an aqueous pulp of said clay isdispersed with a water-soluble sodium silicate dispersant consisting ofoxides of sodium and silicon and water, the dispersed pulp isconditioned for the flotation of colored impurities with collectorreagents selective to said colored impurities and the conditioned pulpis subjected to froth flotation producing a froth which is a concentrateof colored impurities and a machine discharge product containing a clayof reduced impurity content, the improvement which comprises adding asmall amount of a water-soluble salt of a polyvalent metal selected fromthe group consisting of aluminum, manganese and mixtures thereof to saidpulp after it has been dispersed with said sodium silicate but beforethe dispersed pulp has been subjected to froth flotation, said saltbeing added in amount insuflicient to flocculate said pulp, whereby theadverse effect of the possible use of an excessive quantity of sodiumsilicate dispersant is obviated.

2. The method of claim 1 wherein said salt is aluminum sulfate.

3. The method of claim 1 wherein said salt is employed in amount withinthe range of 0.1 to 2 1bs./ton of said clay.

4. The method of claim 1 wherein said collector reagent comprises anemulsified fatty acid and said salt of a polyvalent metal is added andmixed in said pulp containing sodium silicate dispersant before saidemulsified fatty acid is added.

5. The method of claim 1 wherein said collector reagent comprises ahigher fatty acid and finely divided particles different from said clayand capable of being collector-coated by said fatty acid.

6. The method of claim 1 wherein said sodium silicate dispersant isemployed in amount that exceeds a quantity which would produce a machinedischarge product of lower TiO analysis if said flotation were carriedoutwith a smaller quantity of sodium silicate and in the absence of saidsalt of a polyvalent metal.

References Cited UNITED STATES PATENTS 1,541,182 6/1925 Plowman 20951,847,212 3/ 1932 Feldenmeimer 2095 2,158,987 5/1939 Maloney 209-5 X3,337,048 8/1967 Mercade 209-166 X 2,408,656 10/1946 Kirk 2523 132,569,680 10/1951 Leek 2095 X 2,657,183 10/1953 Bechtold 252-3132,894,628 7/1959 Duke 209-166 2,990,958 7/ 1961 Greene 209-166 3,072,2551/1963 Greene 209-l66 2,794,783 6/ 1957 Podschus 2523 13 HARRY B.THORNTON, Primary Examiner R. B. HALPER, Assistant Examiner US. Cl. X.R.209-166

